Solution to "subquery returns more than 1 row" error

Issue

I have one query that returns multiple rows, and another query in which I want to set criteria to be either one of values from those multiple rows , so basicly I want the subquery to look something like this:

select * 
from table
where id= (multiple row query);

Where multiple row query returns multiple rows. So if the values from those rows are 1,2,3 then I want to set id to be 1 or 2 or 3.

Solution

= can be used when the subquery returns only 1 value.

When subquery returns more than 1 value, you will have to use IN:

select * 
from table
where id IN (multiple row query);

For example:

SELECT *
FROM Students
WHERE Marks = (SELECT MAX(Marks) FROM Students)   --Subquery returns only 1 value

SELECT *
FROM Students
WHERE Marks IN 
      (SELECT Marks 
       FROM Students 
       ORDER BY Marks DESC
       LIMIT 10)                       --Subquery returns 10 values

Answered By – Raging Bull

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